Drilling Optimization and ROP Managment

Oil well drilling, a complex and difficult control process, is often characterized by low efficiency. Nowadays the oil well costs are very high and the optimization of the process, in terms of increasing performance and reducing time, is a key factor for success. Various methods are now being utilized to optimize drilling practice indicators such as:

• Conducting Drill-Off tests in order to help obtain the best parameters in drilling operations
• MSE calculation to apply optimum parameters such as WOB and RPM to obtain max ROP and min vibration
• Bit selection and bit performance prediction by using MSE calculations that need mud logging and petrophysical logs to obtain UCS
• Utilizing stability aspects and drilling safe parameter calculation to avoid any vibrations such as bit-bouncing (axial), whirling (lateral), and stick-slip (torsion)

MSE Calculation

The MSE surveillance process provides the ability to detect changes in the efficiency of the drilling system continuously. This has improved performance by allowing the optimum operating parameters to be identified easily and providing the quantitative data needed to cost-justify design changes to extend the current limits of the system.

In this method, data acquired on the field are analyzed to evaluate and identify issues of drilling processes Diagnostic tool has been used whose concept and relative formula were introduced in 1964 (Teale, 1965) MSE is defined as the amount of energy required per unit volume of rock drilled and represents the energy necessary to drill a fixed volume of rock (Kpsi) and the monitoring of MSE can provide information for recognizing dull or damaged bits; select an appropriate bit and WOB and RPM for a bit and rock type, respectively; and avoid the poor mud circulation.

MSE should be kept as low as possible and ROP as high as possible to increase the process’s efficiency; this can be obtained by varying WOB, rotary speed, and mudflow within normal operating limits. Other than identifying performance-limiting factors, MSE can be used as a quantitative measure for assessing benefits associated with redesigning of drilling processes.

Usually drilling engineers want to maintain MSE value as close as possible to a formation’s true compressive strength. Unexpected changes in MSE may indicate changes either in rock properties, drilling inefficiency, or both.

Bit Selection and Bit Performance Prediction

One element of optimizing drilling performance is the optimization of bit selection and operating parameters. This optimization process is often accomplished through trial and error. However, this approach can lead to significant unnecessary expenses and may result in uncertain outcomes, without achieving the desired optimization.

Bit performance optimization processes typically require information on rock strength and other rock properties (such as a MEM) as well as some form of bit performance prediction. To predict performance, it is necessary to understand the characteristics of the material being drilled. Additionally, establishing criteria for determining good or bad performance is essential for the optimization process.

In addition to the need for optimization, there are times when it is critical to reduce the uncertainty of drilling performance prediction. This may be necessary for more confidence in AFE appropriation time estimate for rig sharing agreements, time estimate to work within ”weather windows” and so on.

Pre-drilling bit selection, performance prediction, and optimization based on MEM is predominantly limited to specialists within the bit supplier companies and operations. To a large degree, a high level of expertise and/or reasonably robust and accurate methods is limited. To the extent that accurate bit performance predictions are developed, they are often complex, proprietary, or based on local empirical correlation.

Bit performance prediction may not be globally applicable from surface to great depth, across a typical range of hole sizes, and for all predominant bit types. Bit performance and prediction methods may not be linked or may be sensitive to rig capability (available power and drill string specification). However, this could be a useful capability for optimizing equipment selection and field development planning.

Stability Aspects and Drilling Safe Parameter Calculation

Drilling operations often face significant challenges caused by vibrations. Vibrations accelerate bit wear, and pipe fatigue, and consequently, they can decrease performance. Our software platform includes a dynamic modal analysis which provides drillers with critical rotation speeds and WOB to avoid. Resulting from a validated semi-analytical code, the natural frequencies are calculated for axial, torsion, and lateral vibrations.

The Dynamic Modal Analysis module takes into account several excitation sources such as mass imbalance or steerable motor additional rotation to improve simulation accuracy and avoid bit-bouncing (axial), whirling (lateral), and stick-slip (torsion).

This module provides string modal deflection shapes at single depth for the three types of vibrations and as many modes as necessary, but it also allows multiple-step computations to follow critical vibration variations along a trajectory. Dynamic Modal Analysis results give straightforward operating advice for safer drilling.

The Dynamic Modal Analysis module is both highly useful and easy to handle. It effectively simulates all string vibrations in the frequency domain, offering the following benefits:

• Visualization of drill string modal shapes
• Analysis of drill string dynamic stability
• Drill string high vibration areas identification
• Survey equipment safe positioning
• Critical rotation speed range variations with depth (multiple depths mode)
• Fast and accurate results

Dynamic Modal Analysis module provides fast modeling results to forecast critical RPMs and WOBs for any type of BHA (rotary, RSS, motor, RWD,…). Based on modal analysis of 3D string deflection, this module represents a strong added value to all drilling phases and overall is a powerful asset to string dynamic stability and operating parameters choice. 

Farshad Khoramshahi

Bit and Drilling Optimization Manager
Drill Bits and Downhole Tools